RMX and other reverse MX proposals ALMOST meet the "useful to many,
painful to nobody" criteria for success.
Its pairwise agreement between sending MTAs and domain owners is CLOSE
to being mutual and not disruptive to anyone else;
EXCEPT that it interferes with the everyday common use of relaying via
aliases (with no rewriting of SMTP envelope-from), which means that:
IF my domain starts publishing an RMX record,
THEN mail from my users can no longer reliably be forwarded
without an envelope sender re-write,
SO ALL of my users suddenly can't reach anyone who uses (e.g.)
a .forward file pointing to any RMX-aware MTA, and they have to
send out notes to the effect that "sorry, but I can't reach you
any more unless you adopt something new" but, well, those notes
can't reach their intended recipients either.
While it may be a "good idea" to abolish aliases and .forward files,
actually doing it is a traumatic transition, and it is one that is
NOT under the control of the RMX publisher or the RMX-obeying MTA, but
depends on the cooperation of the vast unwashed body of RMX-non-adopters.
Isn't this a serious impediment at least short-term?
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